This invention relates generally to binocular microscopes. More particularly, the invention is directed to a lens arrangement for illuminating a field of view under microscopic observation at a small angle defined between illuminating and viewing axes or preferably at a zero angle, i.e. along the same optical axis as used for viewing.
Binocular microscopes are used in ophthalmic surgery and in otorhinolaryngologic surgery among other applications. An example of a binocular microscope in the patent literature can be found in U.S. Pat. No. 4,341,435--Lange et al, July 27, 1982. The subject matter disclosed in that patent is hereby incorporated by reference.
In surgical applications, illumination of the surgical site is difficult. Sometimes it is necessary to deeply illuminate a surgical site through a narrow surgical opening. Therefore, it is desirable for the angle between the optical axes of illuminating and observing systems to be as small as possible. If the angle between these axes is too great, the surgical field may not be illuminated to a sufficient depth for many surgical applications.
For example, as shown in FIG. 1 (prior art), in cataract extraction surgery, it is difficult to determine whether any portions of cortex lentis remain at the postaria capsule 240 of an eye after the extraction. The reason for this is that both the crystalline lens 242 and postaria capsule 240 are transparent. A conventional binocular microscope is provided with an illumination system which may illuminate the eye's retina 246 through its iris 250 and postaria capsule 240. The remaining cortex lentis is detected by observing the so-called "red-reflex". This "red-reflex" refers to light reflected from the retina 246 through the postaria capsule which occurs if there are no remaining portions of cortex lentis (all of it was removed during surgery).
In conventional systems wherein the angle 206 between the axis of illumination and the axis of observation is relatively large, the illumination light flux does not sufficiently reach the depth of the surgical site where the retina is found due to obstruction of the illumination light flux by the iris 250 of the eye. Thus, it is difficult to determine whether there are any remaining portions of cortex lentis after performing the cataract extraction.
The problems attendant the prior art will be better understood by continued reference to FIG. 1 (prior art). In a conventional lens arrangement, an illuminating light flux 200 is reflected by a mirror 202 to a peripheral portion 230 of an objective lens 204. This illuminating light flux is converged by lens 204 to form a converged illuminating flux 232 to enter the surgical site (in this case, a human eye). As shown in the drawing, there is an angle 206 which exists between central axes of flux 200 and an observation light flux 208. The larger angle 206 is, the less depth of the surgical site that will be illuminated.
A plan view of lens 204 is shown in FIG. 2 (prior art). This lens is for binocular observation, therefore two portions of observation light flux 208 are shown. The axis of illumination light flux 232 is substantially different from an observation optical axis 210 (shown as a dot in the center of lens 204) directed toward an object to be observed at which both portions of the observation light flux 208 converge.